Conventionally, in the field of process industries, pressure transmitting devices have been used for controlling processes by detecting the variable quantities in processes. The pressure transmitting device is known as a pressure transmitter. The pressure transmitting device is able to measure variable quantities in processes, such as pressure, flow rate, fluid level, specific gravity, and the like, through measurements of differences in pressures between two points or through measurements of absolute pressures. When a variable quantity in a process is measured using a pressure transmitting device, typically that which is to be measured is introduced into the pressure transmitting device through narrow ducts, known as pressure guiding tubes, from both sides of a differential pressure generating mechanism, such as an orifice that is disposed in the process ducting in which flows the liquid, or the like, that is to be measured.
Sometimes, in such a device structure, a solid substance, or the like, becomes adhered to the interior of the pressure guiding tube by that which is to be measured, blocking the pressure guiding tube. Because it becomes impossible to measure accurately the variable quantities for the process when the pressure guiding tube is completely blocked, this can have an extremely large impact on the plant. However, because the pressure is communicated to the pressure transmitting device up until the point when the pressure guiding tube becomes completely blocked, the influence of the blockage does not readily manifest itself in the measured values of the variable quantities in the process. In relation to this process, a remote sealed pressure transmitting device has been created wherein the pressure guiding tubes are not required. However, there is an extremely high number of plants that measure variable quantities of processes using pressure guiding tubes, and thus there are calls for the creation of an on-line diagnosing function for blockages of the pressure guiding tubes.
The technology disclosed in Japanese Patent 3129121 (“JP '121”) is known as a conventional technology for diagnosing a state of blockage of a pressure guiding tube. The technology disclosed in JP '121 is for diagnosing a state of blockage of a pressure guiding tube based on the magnitude of fluctuation of a static pressure and a differential pressure.
The technology disclosed in JP '121, as described above, diagnoses the state of blockage of the pressure guiding tube based on the amplitude of fluctuation of a differential pressure and a static pressure. However, there is a problem in the technology disclosed in JP '121 in that the threshold value that is the criterion for the diagnosis must be adjusted depending on the pressure or the magnitude of the flow rate. The conventional problem areas will be described in detail below.
In a first example of embodiment in JP '121, the diagnosing of a blockage of a pressure guiding tube is performed through detecting increases and decreases in the fluctuation amplitude of a high-pressure-side static pressure and of the fluctuation amplitude of a differential pressure. In the second example of embodiment in JP '121, the diagnosing of the blockage is performed through detecting increases and decreases in the fluctuation amplitude of the low-pressure-side static pressure, in addition to that of the high-pressure-side static pressure and that of the differential pressure. However, the fluctuation amplitudes of the pressure and the differential pressure vary depending on the magnitude of the pressure and of the differential pressure at that time. Moreover, the fact that the fluctuation amplitude will vary depending on the differential pressure means that the fluctuation amplitude varies depending on the flow rate. Consequently, when the first example of embodiment and the second example of embodiment according to JP '121 are applied, it is necessary to adjust, as appropriate, the threshold value for detecting the increases and decreases in the fluctuation amplitudes depending on the pressures and on the differential pressure (the flow rate).
In the third example of embodiment in JP '121, the fluctuation amplitude of the high-pressure-side static pressure, the fluctuation amplitude of the low-pressure-side static pressure, and the fluctuation amplitude of the differential pressure are each calculated, and the diagnosing of the blockage of the pressure guiding tubes is performed based on differences in the individual fluctuation amplitudes. While JP '121 claims the ability to cancel out variations in fluctuation amplitudes due to changes in flow rate, through taking the differences in the fluctuation amplitudes, the canceling effects are limited. For example, the parameter S set forth in JP '121 is the result of subtracting the fluctuation amplitude of the differential pressure from the fluctuation amplitude of the high-pressure-side static pressure. However, the fluctuations in the high-pressure-side static pressure and the fluctuations in the differential pressure are produced through different processes to begin with, and thus vary with some degree of independence. As a result, matching of the scopes of increases or decreases of the fluctuation amplitude of the high-pressure-side static pressure and the fluctuation amplitude of the differential pressure, to enable canceling of the effects of the pressure or differential pressure (flow rate) only occurs in rather limited circumstances, and is limited to cases wherein the change in the fluctuation amplitude due to a change in the flow rate is relatively small.
In a fourth example of embodiment in JP '121, single-sample differences are calculated for the high-pressure-side static pressure, the low-pressure-side static pressure, and the differential pressure, respectively, through sampling the high-pressure-side static pressure, the low-pressure-side static pressure, and the differential pressure, and then the diagnosing of a blockage of the pressure guiding tubes is performed based on a parameter that is obtained through fundamental arithmetic operations on these differences. However, this parameter is also influenced by the pressure and by the differential pressure (the flow rate). The reason why this parameter is influenced by the pressure and the differential pressure (the flow rate) will be explained below.
A single-sample difference in the pressure values can be considered to be an instantaneous value for the pressure fluctuation. As such, it is obvious that a sum or a product of a single-sample difference will be affected by the pressure, or the like. The same is true for differences between single-sample differences, where, for the same reason as in the case in the third example of embodiment in JP '121, the conditions under which the influence of the pressure and the flow rate can be canceled are limited. When it comes to a ratio of single-sample differences, if there is, for example, a relationship wherein the fluctuation on the high-pressure-side static pressure is twice that of the fluctuation of the differential pressure at that time, then it would be possible to cancel the effect of the pressure or differential pressure (flow rate). However, as described for the case of the third example of embodiment of JP '121, the processes by which the fluctuations in the static pressure and by which the fluctuations in the differential pressure are produced are different, enabling them to vary independently, and thus the conditions that satisfy the relationship of the fluctuation of the high-pressure-side static pressure being twice that of the fluctuation of the differential pressure at that time are limited.
As described above, when the technology disclosed in JP '121 is used, the fluctuation amplitudes for the pressures and the fluctuation amplitude of the differential pressure, along with the parameters derived from these fluctuation amplitudes, are affected by the pressure and the differential pressure (the flow rate), and thus it is necessary to adjust appropriately the threshold value depending on the magnitude of the pressure or the flow rate.
The present invention is to resolve the issues set forth above, and thus the object thereof is to provide a pressure guiding tube blockage diagnosing device and blockage diagnosing method able to reduce the need for adjusting the threshold value that is the reference for the diagnosis.